This invention relates to a material handling machine having a material handling element, and in particular, to means for indicating the position of said material handling element relative to the operator's cab of said machine.
Mobile material handling machines, such as front end loaders, include a material handling element such as a bucket. Such material handling machines typically include a vertically adjustable boom structure pivotally connected at one end to the machine, and pivotally supporting at the other end thereof the element which is adapted to dig, carry and discharge a load. Various types of tilt mechanisms or linkages have been developed for controlling tilting movement of the element on the boom for the purpose of disposing the element in various positions, such as digging and dumping positions, to receive and discharge a load respectively.
In material handling machines of the type described, a particular problem is encountered by the operator in properly positioning the material handling element when the element is in a low-level position. This problem manifests itself irrespective of the particular type of tilt or support linkage involved. The problem is presented due to the fact that the linkage connecting the boom and material handling element extends forwardly from the machine's operator's cab and obstructs the operator's view of the material handling element when it is in its low level position. Accordingly, the operator experiences difficulty in properly positioning the element in a selected position such as, for example, a low-level digging position. Specifically, the bottom and cutting edges of the material handling element are usually invisible to the operator. Operations such as stripping and clean-up, which require the material handling element to be level, become very difficult to perform effectively due to the described problem.
Prior attempts to overcome the described problem includes placing a wide horizontal line on the material handling element. The line is in the operator's line of sight. Relative change in the width of the line roughly indicates the relative position of the material handling element with respect to the underlying ground. This method is neither accurate nor does it assure positive indication of direction of the tilt of the material handling element.
In U.S. Pat. No. 3,017,046, there is disclosed a bucket position indicator utilizing a cam provided with two cam surfaces. A cam follower rides along the cam surface during movement of a bucket tilt jack. The cam follower causes the movement of an indicator relative to an indicia point. The indicia marker is set so that when the pointer reaches alignment with the indicia, tilt jack retraction is discontinued by the operator and the bucket is in the position to resume digging operations when the boom is lowered. This device is vulnerable to damage since it is located on the top of the material handling operating cylinder. The device is relatively complex and expensive to manufacture. The altitude of the material handling element is indicted indirectly through movement of the material handling element cylinder rod. Such movement has a non-linear relationship with the altitude change of the material handling element. The cam, cam follower and spring are susceptible to wear. The same size device could not be used for different size machines, which is a further limitation.
In U.S. Pat. No. 4,309,142, there is disclosed apertures provided through the material handling element so that the operator's line of sight will locate the leading edge of the element. Alternatively, a mirror is provided at an upper edge of the material handling element and is attached to the edge of the element by an integral bracket. The mirror is positioned to enable the driver or operator to see the reflection of the leading edge of the element. Like the other prior art devices heretofore discussed, this arrangement also suffers from multiple deficiencies. For example, once the cutting edge of the material handling element is embedded in the ground, it is impossible to know the altitude of the element. When apertures are provided through the element, special reinforcement of the element must be added to maintain structural integrity thereof. When a mirror is employed, it is extremely vulnerable to damage. In large machines, visibility would be very poor due to the increased distance between the operator's cab and the cutting edge of the element. The apertures in the element will most likely become plugged with material. This arrangement further requires sufficient illumination to enable the operator to see the reflection of the element, or to see through the apertures. If the mirror embodiment is employed, this arrangement is relatively complex and expensive.
Accordingly, it is an object of the present invention to enable the machine's operator to visually monitor the position of the material handling element through a relatively simple, easily maintained, and highly accurate arrangement.